1. Field of the Invention
The invention is directed to a torsional vibration damper in a lockup clutch of a hydrodynamic clutch device having an impeller wheel and a turbine wheel, wherein the torsional vibration damper is connected between a turbine shell and a turbine hub of the turbine wheel and includes a drive side damper element connected with the turbine shell, a driven side damper element connected to the turbine hub, and a circumferentially acting spring connected between the drive-side and driven-side damper elements.
2. Description of the Related Art
A prior art torsional vibration damper arranged between a turbine shell and a turbine hub of a turbine wheel is known, for example, from German reference DE 43 33 562 A1. This reference discloses a clutch device constructed with an impeller wheel, a turbine wheel having a turbine shell, and a stator wheel and accordingly acts as a hydrodynamic torque converter. The turbine shell is arranged so as to be rotatable relative to a turbine hub and is connected with a drive-side damper element of the torsional vibration damper. The drive-side damper element is operatively connected with a driven-side damper element via a damping device with energy accumulators acting in the circumferential direction. The radial inner side of the driven-side damper element is fixed with respect to rotation relative to the turbine hub so as to be fixed with respect to rotation relative to it.
Considered as a free oscillating system, the drivetrain of a motor vehicle may be roughly reduced to six masses. It is assumed that the drive, including the impeller wheel, is the first mass, the turbine wheel is the second mass, the transmission input shaft is the third mass, the cardan shaft (including the universal joint, i.e., cardan joint) and differential are the fourth mass, the wheels are the fifth mass and the vehicle overall is the sixth mass. In a free oscillating system with n masses (in this case n=six), it is known that n resonant frequencies occur. However, the first resonant frequency relates to the rotation of the entire oscillating system and is not relevant to vibration damping. The rates of rotation or speeds at which the resonant frequencies are excited depend on the number of cylinders of the drive which is constructed as an internal combustion engine.
Because the drive-side damper element of the torsional vibration damper acts on the turbine shell and the driven-side damper element acts on the driven shaft which, as is known, acts as a transmission input shaft, the torsional vibration damper according to the above-cited DE 43 33 562 A1 is commonly known in technical circles as a "turbine damper" and has the following characteristics:
Because the driven-side transmission element is directly connected with the transmission input shaft, the damping device which connects this damper element with the drive-side damper element acts as if it were connected in series with the elasticity of the transmission input shaft, which elasticity is conditional upon torsion. However, since the stiffness of the energy accumulators of the damping device is much less than that of the transmission input shaft, the transmission input shaft is considered very soft with respect to total rigidity. This softness of the transmission input shaft results in excellent decoupling characteristics.
With respect to the resonant frequencies in the drivetrain, the extensive softness of the transmission input shaft causes the third and fourth resonant frequencies of the five resonant frequencies mentioned above to have greater amplitudes compared to a torsional vibration damper arranged in conventional manner between the piston and turbine hub. However, the third resonant frequency occurs at considerably lower speeds, namely at a speed in the order of magnitude of the second resonant frequency. Accordingly, the third resonant frequency has practically no effect when the lockup clutch is closed already at a very low speed, for example, 1200 RPM. However, no influence can be exerted in this way on the fourth resonant frequency, so that noise may occur when passing through the speed range associated with this resonant frequency.